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1. a small, local, involuntary, muscular contraction, due to spontaneous activation of single muscle cells or muscle fibers.
2. the quality of being made up of fibrils.
3. the initial degenerative changes in osteoarthritis, marked by softening of the articular cartilage and development of vertical clefts between groups of cartilage cells.
Fibrillation on an electrocardiographic tracing. From Fenstermacher and Hudson, 1995.
atrial fibrillation a reentrant cardiac arrhythmia marked by rapid randomized contractions of the atrial myocardium, causing a totally irregular rapid atrial rate. It is recognizable on an electrocardiogram by the absence of P waves and an irregular ventricular response. It may be controlled by drug therapy or cardioversion.
ventricular fibrillation a cardiac arrhythmia marked by fibrillary contractions of the ventricular muscle due to rapid repetitive excitation of myocardial fibers with ineffectual ventricular contraction; on the surface electrocardiogram it is characterized by lack of identifiable QRS complexes. This is a frequent cause of cardiac arrest. An apparatus called a defibrillator is used to alleviate it by delivering an electric shock to the heart muscle; this depolarizes the myocardium and ends the irregular contractions so that the heart can resume normal, regular contractions.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.


An electric shock applied to the heart to terminate a disturbance of its rhythm.
Farlex Partner Medical Dictionary © Farlex 2012


An electric shock applied to the heart to terminate a disturbance of its rhythm.
Medical Dictionary for the Health Professions and Nursing © Farlex 2012
References in periodicals archive ?
CONGRESS countershocks continued to ripple out of the capital the day after the Gujarat Chief Minister Narendra Modi targeted Prime Minister Manmohan Singh in his Independence Day speech at Lalan College, Bhuj.
Initially, 5 cycles of 30 compressions and 2 ventilations with direct current countershocks were performed up to 3 times, following the local EMS protocol.
As the emergency medical technicians wheel the patient through the door, they explain that he has received epinephrine, countershocks, and an endotracheal tube.